The regulation of cadherin-mediated adhesion underlies many morphogenetic processes. Understanding cadherin regulation in embryos has important implications for many developmental diseases, including birth defects, and it will be important for advances in regenerative medicine. The regulation of cadherins also occurs in adult tissues and is involved in many pathophysiological processes including alterations in epithelial transport, inflammation, and vascular remodeling. In particular, downregulation of E-cadherin function or remodeling of adherens junction during the epithelial to mesenchymal transition (EMT) contributes to tumor metastasis, and the ability to slow this process could provide approaches for cancer therapy. Much has been learned in recent years about the cellular processes (eg. membrane trafficking, cytoskeletal dynamics, protein turnover) and signaling pathways that impact on cadherin-mediated adhesion and adherens junction remodeling. In a different area of investigation, a great deal has been learned about the molecular structure of the cadherin homophilic bond. The goals of this proposed project are to bridge the gap between these two areas and elucidate how regulation of adhesion by these various cellular processes and growth factor signaling pathways controls the structure and activity state of the cadherin adhesive bond. Novel tools that will be key to this project are cadherin activating monoclonal antibodies (mAbs) and conformation selective mAbs for different cadherin structural and functional states. The specific aims are: A. Analyze the relationship between the activity state of the E-cadherin at the cell surface and E-cadherin internalization, adherens junction remodeling or disassembly during the epithelial-mesenchymal-transition (EMT), and the growth and spread of human epithelial tumor cells;B. Determine how Paraxial Protocadherin (PAPC) regulates C-cadherin- mediated cell adhesion and cell sorting in the early Xenopus embryo;C. Explore cadherin conformations and three-dimensional structures associated with functional states, including dimerization and activity state, as defined by conformation selective and activating mAbs;D. Analyze cellular and molecular mechanisms controlling cadherin activity states at the cell surface in response to activating monoclonal antibodies and growth factor signaling;using high resolution fluorescence imaging, a structure-function analysis of the cadherin-catenin complex, and the identification of cadherin interacting proteins specifically associated with activity state. An important hypothesis to be tested is that inside-out regulation of the activity state of cadherins at the cell surface participates in many of the cellular events associated with adherens junction remodeling and cadherin downregulation. PUBLIC HEALTH RELEVANCE: Cadherins are cell adhesion proteins, which function to hold cells together in tissues and organs, and cadherin dysfunction can lead to development defects in embryos as well as tumor growth and metastasis in adults. We are trying to understand the way that cadherin protein molecules are switched on and off at the surface of the cell to control their adhesive functions in tissues. Moreover, we are developing methods to detect and control the functional state of cadherins on the cell, which have the potential to be used as diagnostic or therapeutic approaches for the treatment of many diseases, including cancer.